This invention relates to the preparation of an optical fiber payout canister, and, more particularly, to the formation of the base layer of the canister.
Optical fibers are strands of glass fiber processed so that light transmitted therethrough is subject to total internal reflection. A large fraction of the incident intensity of light directed into the optical fiber is received at the other end of the optical fiber, even though the optical fiber may be hundreds or thousands of meters long. Optical fibers have shown great promise in communications applications, because a high density of information may be carried bidirectionally along the optical fiber and because the quality of the signal is less subject to external interferences of various types than are electrical signals carried on metallic wires. Moreover, the glass fibers are strong, light in weight, and made from a plentiful substance, silicon dioxide.
Glass optical fibers are typically fabricated by preparing a preform of glasses of two different optical indices of refraction, one inside the other, and processing the preform to a fiber. The optical fiber is coated with a polymer layer termed a buffer to protect the glass from scratching or other damage. As an example of the dimensions, in the conventional configuration the diameter of the glass optical fiber is about 125 micrometers, and the diameter of the optical fiber plus the polymer buffer is about 250 micrometers (approximately 0.010 inches). A new generation of even finer optical fibers with reduced buffer thickness is becoming available, having a total diameter of about 175 micrometers (approximately 0.007 inches).
For such very fine optical fibers, the handling of the optical fiber to avoid damage that might reduce its mechanical strength properties becomes an important consideration. In one approach, the optical fibers are wound onto a cylindrical or tapered cylindrical bobbin, generically termed a frustoconical bobbin, with many turns adjacent to each other in a side-by-side fashion. To fabricate such a bobbin, a base layer is first wound on the bobbin surface. The base layer has a pattern that defines the winding pattern of the first optical fiber layer, which is wound on top of the base layer. After one optical fiber layer is complete, another layer of optical fiber is laid on top of the first layer, and so on. A weak adhesive is typically applied to the layers of optical fiber to hold them in place. The final assembly of the bobbin and the wound layers of optical fiber is termed a canister, and the mass of wound optical fiber is termed the fiber pack. When the optical fiber is later to be used, the fiber is paid out from the canister in a direction parallel to the axis of the bobbin.
Experience has shown that the form and pattern of the base layer is key to achieving a high-quality canister. The canister is often exposed to a range of temperatures and other environmental conditions during storage and use. Various types of defects can form in the optical fiber pack, such as pop-ups and folds. These defects can lead to failure of the optical fiber during payout, with even one failure resulting in inoperability of the entire system. A well-formed base layer that gives good lateral support to the first layer of optical fiber aids in stabilizing the optical fiber pack against such defects.
There is therefore an ongoing need for an optical fiber base layer that provides good support for the first optical fiber layer, permits the preparation of optical fiber canisters using a range of optical fiber sizes, and is relatively inexpensive. The present invention fulfills this need, and further provides related advantages.